The invention relates to a high frequency module having a waveguide structure, and to a method for producing such a module. The millimeter-wave communication modules according to the invention operate, for example, in the GHz range and are used for the transmission of data in traffic engineering.
For producing metal-ceramic composite structures for waveguide uncouplings in millimeter-wave communication modules, the antenna substrates are soldered on waveguide throughfeeds in microwave housings with a hermetic closure. In currently available manufacturing processes, so-called preforms are used for a hermetic closure which are inserted as intermediate layers between the ceramic cover and the housing. Important criteria for the quality of such connections are their stability with respect to changing temperatures and their reliability in the continuous operation. In addition, the exclusion of moisture from the housing interior plays an important role with respect to the electrical operation.
International Patent Document WO 91/209699 discloses a hermetic closure of ceramic-metallic housings for integrated circuits, in which ceramic housing covers are mounted and soldered by means of gold/tin preforms. Soldering is performed at a temperature below 400° C. by means of a heating electrode which is in contact with the housing. The cover and the housing are pressed on one another during the soldering operation.
A significant disadvantage of previous manufacturing processes is the low positioning tolerance for joining individual modules, which makes automated manufacture more difficult, or even impossible. The construction of waveguide uncouplings using preforms and the registration pins normally used for precise positioning of the housing cover, increases the time required, and is acceptable only in the case of small piece numbers.
One object of the invention is to provide a manufacturing process and a high frequency module with increased positioning tolerances in the automated production of hermetic HF modules.
This and other objects and advantages are achieved by the waveguide arrangement according to the invention, which includes a high-frequency module with a waveguide structure consisting of a housing bottom and a housing cover, preferably made of ceramics. The expansion behavior of the housing bottom and the cover are coordinated with one another. For example, the housing cover will consist of aluminum oxide and the housing bottom will consist of Mo30Cu. An adjusting device is mounted on the housing cover for positioning on the housing bottom. In order to prevent corrosion, the metallic housing is modified by means of a nickel and gold layer.
The adjusting device consists of a photosensitive resist elevation which, starting from the cover surface of the housing, tapers conically. During the mounting, the adjusting device engages in the waveguide. The layer thickness of the adjusting device amounts to approximately 100 to 200 μm. The housing cover and the housing bottom are firmly connected with one another by soldering. For this purpose, solders are preferably used which are galvanically fed into solder depots. The solder is either applied locally to the housing cover surface, which is in contact with the housing bottom, or is fed into ducts that are structured in the cover.
The method according to the invention, for producing a high-frequency module, includes the following steps:                The contact surface of the housing cover is structured with the housing bottom with a first photo resist mask for a galvanic metal deposition;        a gold/tin layer sequence of the solder depot is deposited;        the first photo resist mask is removed;        a second photo resist mask is structured as the adjusting device;        the tin surface is cleaned of oxide;        the housing cover is centered on the waveguide and fixed;        the housing cover is soldered to the housing bottom;        the resist of the adjusting device is removed in a wet-chemical manner.        
The resist of the adjusting device is preferably removed in a wet-chemical process, using a heated potassium hydroxide solution.
A special advantage of the invention is in its simplicity in the case of a manual construction of waveguide throughfeeds. It also permits automatic assembly of the modules for a manufacturing of larger piece numbers.
Another advantage consists of the cost-effective integration of the manufacturing steps in the manufacturing of thin-layer substrates, which constitutes a significant simplification of the assembling process.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.